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摘要
Visible light excitation of [Ru(deeb)-(bpz)(2)](2+) (deeb = 4,4'-diethylester-2,2'-bipyridine; bpz = 2,2'-bipyrazine), in Br- acetone solutions, led to the formation of Br-Br bonds in the form of dibromide, Br-2(center dot-). This light reactivity stores similar to 1.65 eV of free energy for milliseconds. Combined H-1 NMR, UV vis and photoluminescence measurements revealed two distinct mechanisms. The first involves diffusional quenching of the excited state by Br- with a rate constant of (8.1 +/- 0.1) X 10(10) M-1 s(-1). At high Br- concentrations, an inner-sphere pathway is dominant that involves the association of Br-, most likely with the 3,3'-H atoms of a bpz ligand, before electron transfer from Br- to the excited state, k(et) = (2.5 +/- 0.3) X 10(7) s(-1). In both mechanisms, the direct photo-product Br-center dot subsequently reacts with Br- to yield dibromide, Br-center dot + Br- -> Br-2(center dot-). Under pseudo-first-order conditions, this occurs with a rate constant of (1.1 +/- 0.4) X 10(10) M-1 s(-1) that was, within experimental error, the same as that measured when Br-center dot were generated with ultraviolet light. Application of Marcus theory to the sensitized reaction provided an estimate of the Br-center dot formal reduction potential E(Br-center dot/Br-) = 1.22 V vs SCE in acetone, which is about 460 mV less positive than the accepted value in H2O. The results demonstrate that Br- oxidation by molecular excited states can be rapid and useful for solar energy conversion.
- 出版日期2015-7-8
